1. Field of the Invention
The present invention relates to a zoom lens system.
2. Description of the Prior Art
In a zoom lens system for normal use in a camera, cost reduction on a lens system, having the angle-of-view of about 37xc2x0 at the short focal length extremity (the wide angle side), and having a zoom ratio of about 2.5 to 3.5, is required. For example, the zoom lens system, which is proposed by the applicant of the present invention in U.S. Pat. No. 6,078,435, has the zoom ratio of about 2.7; and in such a zoom lens system, a larger zoom ratio and further miniaturization are required without causing an increase of the production costs thereof. Furthermore, the applicant (inventor) has proposed the zoom lens system having the zoom ratio of about 3.5 in U.S. Pat. No. 6,487,023; however, a zoom lens system, such as one disclosed therein, is further required to reduce the production costs.
The present invention provides a zoom lens system of a four-lens-group arrangement which (i) has a large zoom ratio of about 3, (ii) is miniaturized, and (iii) is produced at relatively low costs.
According to an aspect of the present invention, there is provided a zoom lens system including a first lens group having a positive optical power (hereinafter, a positive first lens group), a second lens group having a negative optical power (hereinafter, a negative second lens group), a third lens group having a positive optical power (hereinafter, a positive third lens group) and a fourth lens group having a positive optical power (hereinafter, a positive fourth lens group), in this order from the object. Upon zooming, each of the first through fourth lens groups independently move along the optical axis.
The positive first lens group includes a negative lens element and a positive lens element, in this order from the object.
The zoom lens system satisfies the following conditions:
n1-2 greater than 1.68xe2x80x83xe2x80x83(1)
1.35 less than xcex94X1/f less than 1.50xe2x80x83xe2x80x83(2)
wherein
n1-2 designates the refractive index of the positive lens element of the positive first lens group;
xcex94X1 designates the traveling distance of the positive first lens group from the short focal length extremity to the long focal length extremity; and
f designates the focal length of the entire zoom lens system at the short focal length extremity.
The zoom lens system of the present invention preferably employs an inner-focus type focusing mechanism in which focusing from infinity to an object at a closer distance is performed by moving the negative second lens group toward the object.
In the zoom lens system of the present invention, the ratio of the traveling distance of the positive first lens group to the traveling distance of the negative second lens group upon zooming is always constant, and the zoom lens system preferably satisfies the following condition:
3.50 less than xcex94X1/xcex94X2 less than 6.00xe2x80x83xe2x80x83(3)
wherein
xcex94X2 designates the traveling distance of the negative second lens group from the short focal length extremity to the long focal length extremity.
In the zoom lens system of the present invention, the ratio of the traveling distance of the positive third lens group to the traveling distance of the positive fourth lens group upon zooming is always constant, and the zoom lens system preferably satisfies the following condition:
0.92 less than xcex94X3/xcex94X4 less than 0.98xe2x80x83xe2x80x83(4)
wherein
xcex94X3 designates the traveling distance of the positive third lens group from the short focal length extremity to the long focal length extremity; and
xcex94X4 designates the traveling distance of the positive fourth lens group from the short focal length extremity to the long focal length extremity.
The negative second lens group preferably includes a negative meniscus lens element having the convex surface facing toward the object, a negative lens element and a positive lens element, in this order from the object.
The positive third lens group preferably includes a positive lens element having a convex surface on the object-side thereof, and a negative lens element having a concave surface on the object-side thereof, in this order from the object.
The positive fourth lens group preferably includes a positive lens element having a convex surface on the image-side thereof, a positive lens element and a negative meniscus lens element having the concave surface facing toward the object, in this order from the object.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2002-196127 (filed on Jul. 4, 2002) which is expressly incorporated herein in its entirety.